What about the mechanical advance? Say you get about 18 at idle with the vac disconnected. Rev the engine up, vac still unhooked, what have ya got now. Just for an example. 20 degress initial, rev it up 20 more for a total of 40 with the mech, now hook up the vac and see if it goes to about 50-60 degrees total advance. Sounds like the mechanical weights in the dizzy may be stuck.